Batch charger for cold top electric furnace

ABSTRACT

A batch charger has a telescopic belt conveyor with a vertical take-up system for the belt when the conveyor retracts. The conveyor may pivot and/or shift laterally besides the furnace on a track. Fixed silos are positioned to refill an on conveyor bin while it is pivoting.

FIELD OF THE INVENTION

[0001] This invention relates to an apparatus for delivering anddistributing powdered materials over a surface. More particularly, itrelates to the charging of a furnace eg. for the production of moltenglass, with silica and the like by distribution of such materials overthe upper surface of the melt. As a specific embodiment, the inventionrelates to a conveyor feed system that is configured to occupy a reducedfloor area within a melt-shop. As a further embodiment the feed systemis configured to deliver its charge while it is, itself, being refilled.

BACKGROUND TO THE INVENTION

[0002] In furnaces of the continuous feed type, particularly glassmelters operating on a cold top basis, the charging of raw materialsinto the crucible must be effected in a controlled and evenlydistributed manner. In glass furnaces, silica, lime and other componentsare continuously distributed over the top surface of the melt so as toprovide a heat-conserving, insulative, upper layer floating on the melt.The level of this layer should be closely controlled to provide properfurnace operation. By adjusting the flow of current to electrodes withina furnace, the thickness and the rate of melting of the non-meltedtop-insulating layer should be maintained within target values over theentire top surface of the furnace. If the furnace has hot spots wheremelting is more rapid the rate of charge for such areas should beadjusted to maintain blanket thickness.

[0003] A consideration in the design of chargers for furnaces is thefloor area available for operating the furnace. Most chargers extendoutwardly beyond the periphery of the furnace, consuming valuable floorspace. With longitudinally feed systems such as screw and beltconveyors, the external space occupied by the charger can approach andexceed the width of the top surface of the furnace. This situationarises from the need to extend and retract the screw or conveyor so thatits discharge end can be located over all portions of the upper surfaceof the melt.

[0004] Chargers of this type can be located on a pivot to permit thedischarge end of the conveyor to swing over the width of the topsidesurface. Or they may be mounted on a rail providing transversedisplacement of a charger having a fixed orientation with respect to thefurnace crucible. In either case, providing access to the full area ofthe topside surface of the melt is an essential requirement.

[0005] The extension of such charging apparatus over floor spaceadjacent to the furnace consumes valuable plant real estate. It would behighly desirable to provide a furnace charger, which is able to feedmaterials over the entire topside surface area of a furnace withoutconsuming a substantial amount of floor area adjacent to the furnace.This invention addresses that objective.

[0006] A further concern in this art is the time that a conveyor spendsin charging a furnace. Typically, conveyor systems carry an on-boardsupply of charging materials in a bin that must be refilledperiodically. To refill this bin, such conveyor systems are moved to arefilling station. Presently, attendance at such a refilling station is“downtime” when the conveyor is not engaged in charging the furnace. Afurther object of the present invention is to reduce the proportion ofdown-time arising from refilling an on-conveyor supply bin.

[0007] The invention in its general form will first be described, andthen its implementation in terms of specific embodiments will bedetailed with reference to the drawings following hereafter. Theseembodiments are intended to demonstrate the principle of the invention,and the manner of its implementation. The invention in its broadest andmore specific forms will then be further described, and defined, in eachof the individual claims, which conclude this Specification.

SUMMARY OF THE INVENTION

[0008] According to the invention in one aspect, a charger for a furnacehaving a crucible with a topside surface over which is to be distributedcharging materials includes a belt conveyor with a discharge endsupported by a telescopic boom as part of a telescopic conveyorassembly. The charger is positioned on support means located along theperiphery of the surface to be charged. This support means may comprisea pivoting base that allows the discharge end of the conveyor to bepositioned over substantially the entire or greater part of topsidesurface to be charged. Or it may comprise a carriage mounted on a railfor moving the conveyor boom transversely along the periphery of thefurnace. Such rotational or translational displacement combined with theextension and contraction of the telescopic boom enable the dischargeend of the belt conveyor to be positioned over substantially the entiretop surface of the furnace which is to be charged to the extent requiredfor cold-top furnace operation.

[0009] To minimize the footprint of floor space adjacent to the furnaceoccupied by the charger, the conveyor belt along the periphery of thefurnace is redirected vertically by a vertical take-up system. Thus thebelt has a horizontal run for the greater part of the span of its extentover the surface of the melt; and a vertical extent for the length ofits vertical take-up. Conveniently, the vertical take-up over-lies or isadjacent to the support means on the side remote from the furnace,limiting the extent to which the conveyor charger assembly extendshorizontally beyond the furnace periphery when its discharge end isretracted to a position near to the support means. As the boom for thehorizontal extension of the conveyor is telescopic, the extension ofcomponents of the charging system over valuable floor space is minimizedwhen the conveyor is in its retracted position.

[0010] The belt take-up system may carry the taken-up portion of thebelt in a generally vertical direction, while still tensioning the belt,(which is intended to be still running during take-up), through the useof weights, powered cylinders or the like which serve as tensioningmeans. Alternatively or additionally, the belt take-up system can imposeon the belt a sinuous path of optionally variable amplitude, shorteningthe overall height of the belt take-up system.

[0011] The belt take-up system need not be located centrally over thesupport means. Allowing that it is desirable to counter-balance thetorque on the support means that arises from the boom, particularly inits extended state, the belt take-up system can be located outwardlyfrom the center of the support means. This will provide a counter-torquereducing the torque developed by the boom on the support means.

[0012] As one of the objects of the feed system is to provide for acontinuous charging operation, a supply bin for the conveyor, carried bythe charger system, may be replenished at regular intervals from a fixedsupply silo source. Access to the supply silo can be intermittent solong as the on-charger supply bin is sufficiently filled to providecharge continuously to the conveyor. By providing a pivoting supportmeans such recharging access to the supply silo can be made convenientlyavailable when the charger is in a specific location. Thus refilling ofthe supply bin can occur while the telescopic boom is engaged inextending or contracting and/or pivoting in the course of distributing acharge over the melt.

[0013] In the case of a charging system relying on a rail-supportedtravelling carriage moving along one axis -y- as the support means, tworeloading stations with two supply silos may be provided. These may beprovided at the two outer ends of the carriage tracks. Replenishment ofthe on-charger supply bin can thereby be effected while the furnace isbeing fed from either one of the ends of the carriage tracks.

[0014] Combined with a charging system incorporating a pivoting supportmeans, two such end-located silos may recharge the on-charger supply binwhile the pivoting support means is delivering a charge over virtuallyall of the surface of the melt. In this manner “down-time” is minimizedto nearly its absolute limit.

[0015] The foregoing summarizes the principal features of the inventionand some of its optional aspects. The invention may be furtherunderstood by the description of the preferred embodiments, inconjunction with the drawings, which now follow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic side view of a prior art conveyor-typecharger with a non-telescopic boom in the retracted (dotted) andadvanced (solid) positions.

[0017]FIG. 2 is a schematic side view of a modified charger from that ofFIG. 1 wherein the boom is a two-part telescopic unit in the fullyadvanced position.

[0018]FIG. 3 is a schematic detailed side view of the charger showing avertical take-up for the conveyor belt and conveyor rollers.

[0019]FIG. 3A is a plan view of the roller system supporting the belt ofthe conveyor.

[0020]FIG. 3B is a partial face view of the roller system of FIG. 3A, inposition beneath a conveyor belt.

[0021]FIG. 4 is a schematic plan view of the view of FIG. 3 wherein theconveyor assembly is pivotally mounted showing sufficient span for thecharging coverage to cover substantially the entire furnace top surfaceachievable by both pivoting the conveyor assembly and extending thetelescopic boom over its full range.

[0022]FIG. 5 is a system wherein the conveyor assembly of FIG. 4 can beshifted along a furnace-side track to an alternate corner locationwhereby the entire furnace surface can be accessed by the chargerwithout any pivoting of the conveyor.

[0023]FIG. 6 is a schematic plan view of a conveyor assembly as in FIG.4 wherein the end of the conveyor belt has access to the entire topsidesurface of the furnace through a combination of pivoting and translationalong the track.

[0024]FIG. 7 is a schematic plan view as in FIG. 6 wherein the end ofthe conveyor has access to only 90% of the topside surface of thefurnace.

[0025]FIG. 8 is a plan view of a pivoting and translating conveyorassembly delivering a charge to an inner region on the upper surface ofa furnace melt.

[0026]FIG. 9 is a schematic side view of the charger of FIG. 4 showing acorner-located stationary silo serving as a supply bin accessing anon-conveyor bin to refill the on-conveyor bin with charge material.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] In FIG. 1 a furnace 1 has electrical heating electrodes 2embedded in a hot silica melt 3. Over the top surface of the melt 3 is apowder blanket or crust of dry charging material 4.

[0028] Along a side of the furnace 1 a prior art charging assembly 5includes a rail-mounted carriage 6, a retractable prior art conveyor 7and an on-carriage storage bin 16 for feeding charging material to theprior art conveyor 7.

[0029] The prior art conveyor 7 may be advanced as in FIG. 1 orretracted as shown in dotted outline to extend over the entire surfaceof the melt 3. Access to the melt 3 is provided by a sidewall slot 8 inthe wall 9 of the furnace 1. The carriage 6 allows the prior artconveyor 7 to shift laterally across the surface of the melt 3. Theprior art conveyor 7 in FIG. 1 is non-telescopic.

[0030]FIG. 1 represents a prior art system wherein extended space mustbe provided adjacent the furnace wall 9 for the charging system toextend and withdraw the conveyor 7 over the span of the melt 3 surface.The space occupied adjacent the furnace is designated by the length“L_(o)”

[0031] In FIG. 2 a telescopic conveyor assembly 11 with a telescopicboom according to the invention is shown. In this case the carriage 6 isremoved partially back from the furnace wall 9 and access to the surfaceof the melt 3 is obtained by extension and retraction of the travellingboom portion 10 a of the telescopic conveyor 11 assembly.

[0032] The travelling boom 10 a is carried by the support boom lob andincludes an endless circulating belt 12. Within both the travelling andsupport booms are conveyor support rollers 30. While the conveyorsupport rollers 30 within the travelling boom 10 a may be fixed throughbearings to the travelling boom 10 a, the rollers 30 within the supportboom 10 b are linked as by link bars 31, chains or the like, and arecarried by side roller bearings 32 constrained within tracks 33 withinthe support boom 10 b that allow the rollers 30 to be shifted along thetracks 33.

[0033] Upon retraction of the travelling boom 10 a the belt 12 isredirected vertically into a belt-take up system 13 as shown in FIGS. 2and 3. Within this system 13 the belt 12 optionally passes sinuouslyover take-up rollers 14, 14 a.

[0034] The axes of the vertically displaceable take-up rollers 14 aredisplaceably mounted within guides (not shown) to allow for theirvertical displacement. Tensioning means such as weights 44, springs (notshown) or the like are connected through cables 17 to the take-uprollers 14, drawing on the take-up rollers 14 to maintain tension in thebelt 12. The belt take-up system 13 permits the belt 12 to passthere-through under continuous tension while the conveyor assembly 11delivers charge material 4 to the melt 3 surface.

[0035] When the travelling boom 10 a is retracted, the conveyor supportrollers 30 must be accommodated. A roller vertical take-up system 34 maybe provided with a lifting shaft 35 positioned to draw the supportrollers 30 upwardly. As the conveyor belt 12 is drawn vertically by thebelt take-up system 13, the support rollers 30 are simultaneously drawnupwardly, nested within one portion of the sinuously deployed belt 12,of FIG. 3.

[0036] Mounted on the carriage 6 is an on-carriage bin 16 that suppliescharge material 4 to the belt 12 through a feed tube 18 by gravity flowor equivalent delivery means. The top of the on-carriage bin 16 is opento permit this bin 16 to be refilled.

[0037] In FIG. 4 a pivoting version of the charging system of FIG. 2 isshown in plan view with the travelling boom 10 a extended to its limitin dotted outline and fully retracted in solid outline. A pivotingtelescopic charger mounted at a single location at a corner on one sideof a furnace is shown as having virtually full access to the surface ofthe melt 3 within the arcs 39 a, 39 b defined by the end 20 of theconveyor belt 12 when fully extended and retracted. The approximateoutward extent of the charger from the furnace 1 in FIG. 4 is indicatedby “L”.

[0038] In FIG. 5 a non-pivoting carriage 6 (in solid outline) ispositioned at the limit of a laterally-extending track 19 permitting theend 20 of the travelling boom 10 a to extend fully along one sideboundary of the melt 3 surface. Using the laterally extending track 19,the telescopic conveyor assembly 11 can, by being repositioned along thetrack, access the entire top surface of the melt 3 without any provisionfor the assembly 11 to swing or pivot. Again, the approximate extensionof the translationally positioned charging system of FIG. 5 beyond theside of the furnace 1 is indicated by “L”.

[0039] In FIG. 6 access to the surface of the melt 3 is achieved by acombination of pivoting and lateral translation of the conveyor assembly11. The surface of the melt 3 accessed from a first corner location 21in FIG. 6 spans less than the full surface area of the melt 3. Two arcs18 a, 18 b are shown representing the path of the end 20 of the pivotingtravelling boom 10 a in its extended and retracted configurationrespectively based on the corner location 21. Area 24 is not accessiblefrom location 21. Coverage of virtually all of the balance of the entiresurface may be achieved by the shifting the telescopic conveyor assembly11 along the track 19 to the opposite side of the furnace 1 to another,second, position 22. This is shown (schematically) in FIG. 6 by the(dotted) circular outline of the on-carriage bin 16 and conveyorassembly 11. From this second position 22, the end 20 of the travellingboom 10 a may swing over extended and retracted arcs 23 a, 23 b thatpermit access to the non-directly accessible area 24 on the surface ofthe melt 3 not accessed from the first position 21. Extension of thecharging system of FIG. 6 beyond the side of the furnace as depicted isindicated by “L”.

[0040] Taking the outward extension length “L_(o)” of a standard,non-telescopic conveyor (as in FIG. 1) as 100%, normalizing to astandard square furnace size and assuming as an example that thetravelling boom 10 a and support boom lob overlap by 20% when thetravelling boom 10 a is fully extended, the configuration of FIG. 4occupies an extension length “L” that is 87% of that of FIG. 1. Withoutthe pivoting feature and relying on displacement of the carriage 6 as inFIG. 5 the value of “L” would be 70% of L_(o). The value of L for FIG. 6is 62% of L_(o). Thus substantive and progressive reductions in thefloor-space occupied by the charging system have been demonstrated.

[0041] A further reduction in L can be achieved by moving the track 19even closer to the furnace 1 so that arcs 18 b and 23 b fall short offull coverage of the melt 3, creating an inaccessible zone 37 on thesurface of the melt. This is shown in FIG. 7. By permitting aninaccessible zone 37 to exist that extends inwardly from the furnacewall 9 by, for example, 10% of the width of the (square) melt 3 surface,the track 19 may be closed-up towards the side of the furnace 1 toreduce the outward extension length “L” in FIG. 7 to % of the value ofL_(o).

[0042] The inaccessible zone 37 of FIG. 7, defined in part by arc 40 b,is of such a limited size as will not, under normal conditions, impairthe operation of a cold-top electric furnace because of the capacity ofthe charging material 4 on the surface of the melt 3 to redistributeitself due to thermal convection currents within the melt 3 as thecharging material 4 floats on the molten glass surface.

[0043] The degree to which such an inaccessible zone 37 may be permittedcan be adjusted to the circumstances under which presence of a moderate“hot spot” can be tolerated.

[0044] In FIG. 8 the furnace 1 is rectangular, rather than square, as inFIGS. 4 to 7. FIG. 8 shows a rectangle with a 2:1 ratio. A higher ratiois possible, but the travel time to traverse the larger dimension shouldbe limited to ensure that blanket replacement occurs relativelypromptly.

[0045] The space savings advantage of FIG. 6 is not affected bystretching the square of FIG. 6 into a rectangle.

[0046] Although the end 20 of the belt 12 is shown in FIGS. 4 to 7 asspanning the full width of the furnace 1 from wall to wall, this wasdepicted for illustrative purposes. The end 20 of the belt 12 need not,however, extend fully to the furnace walls 9. Instead, as shown for FIG.8, the end 20 of the conveyor assembly 20 can access an inner portion 3Aof the surface of the melt, bounded by a non-directly accessible border28 that is not precisely accessible for direct delivery of chargingmaterial 4. Nevertheless, the ability of the charging material 4 toredistribute itself locally over the surface of the melt 3 will allowthe border 28 to be adequately supplied with a charge. Further, it ishighly desireable to avoid feeding the charge 4 against the furnacewalls 9 as this will wear the refractory lining of such walls 9.

[0047] The value for “L” in FIG. 8, wherein reliance is placed onself-redistribution of the charging materials, is similarly reduced fromthe value of L_(o) as achieved in FIGS. 6 and 7.

[0048] In FIG. 9 a stationary supply bin 24 is shown feeding chargematerial 4 to the on-carriage bin 16 through a conduit 25 whichterminates at a delivery point which is above the center of rotation forthe pivoting carriage 6. This stationary supply bin 24 may be locatedconveniently at a recharging station 21 or 22 as in FIGS. 6 and 7 fromwhich the pivoting telescopic conveyor assembly 11 may cover substantialportions of the surface of the melt 3. This will allow time for theon-carriage bin 16 to be refilled. Areas of the melt surface notaccessed from the recharging stations 21 and 22 may be accessed by thetranslational shifting of the carriage 6 to intermediate locations,relying on the on-carriage bin 16 to supply charge material 4 to theconveyor assembly 11 during the off-station furnace charging interval.

[0049] A major advantage of supplying charging material 4 to the melt 3by way of a pivoting action delivered from two base locations 21, 22 isthat the system can, for most of its operation, deliver chargingmaterial 4 to the melt 3 while the on-carriage bin 16 is being chargedfrom a stationary supply bin 24. By using dual stationary supply binspositioned to render the first 21 and second 22 end positions of FIG. 6as charging stations, the time during which the on-carriage bin 16 isnot being recharged can be reduced to a minimum while, at the same time,optimizing the space consumed by the batch charger system of theinvention.

[0050] In the foregoing disclosure various motors and controls will bepresent in order to operate the conveyor, the belt take-up system, thetelescopic boom and the rail carriage, etc. Not shown for purposes ofsimplication, their incorporation into the system will be apparent tothose skilled in the art.

[0051] On the basis of the foregoing arrangement, a new and more compactcharging system may be constructed for charging a surface such as thatof a furnace with charging material.

[0052] Conclusion

[0053] The foregoing has constituted a description of specificembodiments showing how the invention may be applied and put into use.These embodiments are only exemplary. The invention in its broadest, andmore specific aspects, is further described and defined in the claimswhich now follow. These claims, and the language used therein, are to beunderstood in terms of the variants of the invention which have beendescribed. They are not to be restricted to such variants, but are to beread as covering the full scope of the invention as is implicit withinthe invention and the disclosure that has been provided herein.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A charger for a furnacehaving a melt with a topside surface over which is to be distributedcharging materials comprising: 1) a belt conveyor with a discharge endsupported by a telescopic conveyor assembly and carried on support meanslocated laterally to the surface to be charged. 2) a belt within theconveyor which belt has a horizontal run over the surface of the meltand a vertical extent proximate to the support means whereby the belt isredirected vertically; 3) a vertical take-up system to support andmaintain tension within the belt while it is redirected vertically whilerunning.
 2. A charger as in claim 1 comprising take-up rollers withinthe vertical take-up system and weights coupled to such rollers tomaintain tension on the belt.
 3. A charger as in claim 1 wherein thebelt within the take-up system follows a sinuous path to thereby shortenthe overall height of the belt take-up system.
 4. A charger as in claim1 wherein the belt take-up system is positioned outwardly from thecenter of the support means on the side opposite the boom to provide acounter-torque, reducing the torque developed by the boom on the supportmeans.
 5. A charger as in claim 1 comprising an on-conveyor supply binfor the telescopic conveyor assembly, carried by the support means, anda fixed silo which is positioned to supply charging materials to theon-conveyor supply bin while the telescopic conveyor assembly is engagedin distributing charging materials over the top-side surface of thecrucible.
 6. A charger as in claim 5 where the support means is apivoting support means.
 7. A charger as in claim 5 wherein the supportmeans is mounted on tracks with two outer ends the charger comprisingtwo fixed supply silos respectively provided at the two outer ends ofthe tracks to permit the supply of charge to be delivered to theon-conveyor supply bin at two locations.
 8. A charger as in claim 7wherein the support means is a pivoting support means, and said dualsilos are positioned to re-charge the on-charger supply bin while thetelescopic conveyor assembly is being pivoted over the topside surfaceof the crucible.
 9. A charger as in claim 1 wherein the support means isa pivoting support means to permit the telescopic conveyor assembly tobe pivoted, and the support means is positioned so that, combined withthe extension and contraction of the telescopic conveyor assembly, thedischarge end of the belt conveyor will be positionable oversubstantially the entire topside surface of the melt which is to becharged.
 10. A charger as in claim 1 wherein the support means is apivoting support means to permit the telescopic conveyor assembly to bepivoted, and the support means is positioned so that, combined with theextension and contraction of the telescopic conveyor assembly, thedischarge end of the belt conveyor will be positionable oversubstantially the entire topside surface of the melt which is to becharged less a non-directly accessible area within which the chargingmaterials will be delivered by self-redistribution.
 11. A charger as inclaim 1 comprising a rail system carrying the support means for movingthe telescopic conveyor assembly transversely along the periphery of thefurnace whereby such translational displacement of the support meansalong the rail system, combined with the extension and contraction ofthe telescopic conveyor assembly, enable the discharge end of the beltconveyor to be positioned over substantially the entire topside surfaceof the melt which is to be charged.
 12. A charger as in claim 11comprising a rail system carrying the support means for moving thetelescopic conveyor assembly transversely along the periphery of thefurnace whereby such translational displacement of the support meansalong the rail system, combined with the extension and contraction ofthe telescopic conveyor assembly, enable the discharge end of the beltconveyor to be positioned over substantially the entire topside surfaceof the melt which is to be charged less a non-directly accessible areawithin which the charging material will self-redistribute.
 13. A chargeras in claim 1 wherein the support means is a pivoting support means topermit the telescopic conveyor assembly to be pivoted and said supportmeans comprises a rail system for moving the support means transverselyalong the periphery of the furnace whereby, by combining translation ofthe support means along the rail system, with the pivoting and extensionand contraction of the telescopic conveyor assembly, the discharge endof the belt conveyor may be positioned over substantially the entiretopside surface of the melt which is to be charged.
 14. A charger as inclaim 13 comprising a rail system carrying the support means for movingthe telescopic conveyor assembly transversely along the periphery of thefurnace whereby such translational displacement of the support meansalong the rail system, combined with the extension and contraction ofthe telescopic conveyor assembly, enable the discharge end of the beltconveyor to be positioned over substantially the entire topside surfaceof the melt which is to be charged.
 15. A charger as in claim 14comprising a rail system carrying the support means for moving thetelescopic conveyor assembly transversely along the periphery of thefurnace whereby such translational displacement of the support meansalong the rail system, combined with the extension and contraction ofthe telescopic conveyor assembly, enable the discharge end of the beltconveyor to be positioned over substantially the entire topside surfaceof the melt which is to be charged less a non-directly accessible areawithin which the charging material will self-redistribute.
 16. A chargeras in claim 1 wherein the support means is a pivoting support means topermit the telescopic conveyor assembly to be pivoted and said supportmeans comprises a rail system for moving the support means transverselyalong the periphery of the furnace whereby, by combining translation ofthe support means along the rail system, with the pivoting and extensionand contraction of the telescopic conveyor assembly, the discharge endof the belt conveyor may be positioned over only between 90% and 100% ofthe entire topside surface of the melt which is to be charged.
 17. Acharger as in claim 9 comprising an on-conveyor supply bin for thetelescopic conveyor assembly, carried by the support means, and a fixedsilo which is positioned to supply charging materials to the on-conveyorsupply bin while the telescopic conveyor assembly is engaged indistributing charging material over the topside surface of the melt. 18.A charger as in claim 13 comprising an on-conveyor supply bin for thetelescopic conveyor assembly, carried by the support means, and a fixedsilo which is positioned to supply charging materials to the on-conveyorsupply bin while the telescopic conveyor assembly is engaged indistributing charging material over the topside surface of the melt. 19.A charger as in claim 1 comprising rollers to support the belt conveyor,the rollers being interconnected by articulated links and wherein thecharger includes a roller-take-up system to elevate a portion of therollers vertically when the telescopic conveyor assembly is retracted.